Increasingly, the HVAC industry has resorted to locating heating, ventilating and air conditioning equipment on the exteriors of the structures which the systems are intended to service. For example, it is now commonplace, particularly in commercial installations, to mount HVAC equipment on the roof of a structure or on a pad adjacent to the structure.
The benefits of this practice are several. Perhaps the most prominent one is the fact that with exterior location of HVAC equipment, valuable interior floor space within a building which would normally be used to house the HVAC equipment is freed for other usages. Furthermore, because developers tend to conserve the interior space devoted to HVAC equipment, oftentimes internally mounted HVAC equipment is located in cramped quarters, making it difficult to service. This problem is overcome by mounting the HVAC equipment on the exterior of the structure to be serviced by such equipment, making access to it for servicing a much simpler job.
One difficultly encountered in mounting HVAC equipment on the exterior of a structure that it is to service resides in the possible ingestion into the system of foreign substances found in the ambient. For example, ingestion of rainwater may result in corrosion problems in the equipment. In some types of operations, ingestion of rainwater may also cause operational difficulty in operating the HVAC system.
In HVAC equipment such as furnaces which burn a combustible fuel, another difficulty presents itself. Furnaces typically have two ports to their surroundings. One port serves as an inlet for combustion air while the other port serves as an outlet for the products of combustion resulting from the fuel consumed by the furnace. Not untypically, such ports are located in spaced relation to one another to prevent products of combustion from being drawn into the inlet for the combustion air which, by reason of their composition, could reduce the oxygen content of the inlet combustion air stream and thereby affect the combustion process. At the same time, when the combustion air inlet and the exhaust outlet are located in substantially spaced relationship, difficulties associated with a difference in pressure at the two ports may deleteriously affect the combustion process. For example, exteriorly mounted units are exposed to the wind. Wind currents are not necessarily uniform at two spaced locations, particularly in urban areas where the presence of buildings or other structures may cause swirling winds to occur.
As a result, if the wind causes the pressure at the exhaust outlet to be greater than that at the combustion air inlet, there will be back flow of combustion gas toward the combustion chamber of the furnace. This may cause choking of the combustion process within the furnace which, in turn, can result in unconsumed hydrocarbon fuel ultimately being discharged to the ambient. Similarly, if the wind causes the pressure at the combustion air inlet to exceed that at the exhaust outlet, the resulting rush of air through the combustion chamber may cause partial or entire extinguishing of the flame within the combustion chamber. This, also, results in the discharge of unconsumed fuel to the ambient. Either occurrence will also affect the efficiency of the furnace and thereby interfere with the ability of the equipment to perform its intended, function within the HVAC system.
The present invention is directed to overcoming one or more of the above problems.